Before being jettisoned or thrown into the sea, for example from airplanes or helicopters, such underwater listening buoys form compact units comprising radio equipment, disposed in watertight bodies, and electro-acoustic equipment. On contact with the water, the electro-acoustic equipment becomes detached from the radio equipment, while remaining connected thereto by a suspension link which is both electrical and mechanical, and descends into the water to a predetermined depth. This link consists conventionally of a coiled cable. The radio equipment is mechanically and electrically connected to an antenna which radiates Hertzian waves toward an aircraft in which they are received and processed.
The essential requirement involved in jettisoning a unit of the aforesaid type is that the unit must not be damaged when it comes into contact with the water. For use in jettisoning units of this type, there have hitherto been employed either rotochutes of the autogyro type, or parachutes, typically of cruciform type. Known jettisoning devices of the type comprising a cruciform parachute sometimes comprise an inflatable float associated with the parachute, there being contained in the float a radiating wire which is tensioned when the float is inflated, and which performs the function of an antenna. Such a device is relatively simple, involves little cost in regard to the antenna, is of small overall dimensions when folded, and ensures good insulation against sea water. However, it has disadvantages. The float forms a relatively considerable or large wind catch, so that the buoy is caused to drift, and this results in errors in location. This considerable wind catch also brings about a considerable inclination of the antenna, which is unfavorable to the radiation of the antenna, and can result in induced noise on the cable carrying the electro-acoustic equipment, whereby the sensitivity of the latter is reduced. Although it is economical in regard to the antenna, such prior devices are costly because they necessitate the use of a considerable quantity of waterproof fabric, and usually can only be produced by specialized labor. In addition, the known inflatable floats are generally inflated by active inflating devices such as compressed air bottles, which accordingly increases the cost of production. Such floats generally consist of a sphere on which there is mounted a cone, so that they are difficult to produce. If they are of tetrahedral form, they frequently have insufficient reserve of buoyancy if the foot of the antenna is positioned below the level of the sea.
The basic object of the present invention is to obviate the aforesaid disadvantages and to provide a generally improved jettisoning and flotation device, particularly for acoustic buoys, which device, while being of low cost, has a relatively small wind catch.
Generally the invention comprises a jettisoning and flotation device for a suspended load, particularly an underwater listening buoy, comprising a parachute from which the load is suspended, and at least one inflatable float intended to maintain the load at a predetermined depth, characterized in that the float consists of a pillow-shaped ballonet fixed in the central part of the parachute and extended by an inflation sleeve acting under the effect of the superatmospheric air pressure generated by the parachute in its descent, the sleeve being stretched by a tension member whose ends are fixed to the free end of the sleeve and to the load, respectively. Such a pillow-shaped ballonet, being generally of relatively small vertical dimension relative to its lateral dimensions, is substantially less affected by wind than are the known devices of the previously described types.
The invention also comprises improved arrangements for suspending the load from a parachute during descent and releasing the load upon entry into the water, to be suspended at a predetermined depth below the float, being connected to the float electrically and mechanically. Thus, the invention also comprises a jettisoning and flotation device for a suspended load, including a parachute from which the load is suspended, and an inflatable float intended to maintain the load at a predetermined depth after entry into the water, the load being fixed to the parachute by means of a sling fixed at one end to the parachute suspension lines and linked to the load at the other end through a releasable fastening arrangement which is constructed to release the load after entry into the water such that the load can be suspended at a predetermined depth below the float, being coupled to the float. In one embodiment, the releasable fastening device releases the connection between the load and the suspension lines of the parachute, and suspends the load beneath the float by an electrical conductor and a resilient link. The release of the load is governed in part by a link coupled to the releasable fastener and the lower end of the inflation sleeve. In another embodiment, the load is in the form of a tubular envelope, and the releasable fastening device is formed in the cover or lid for the envelope, the parachute sling being coupled to this cover, and the cover being releasable upon entry of the envelope into the water, such that the envelope is free to descend further to a predetermined depth governed by a cable coupling the load to the float carried by the parachute.
Other and further objects, features and advantages of the invention will become apparent to those skilled in the art from the ensuing description of preferred embodiments, taken in conjunction with the accompanying drawings.